The present invention relates generally to the field of medical catheters and more specifically to a dual catheter assembly. A method of separately withdrawing fluids from major blood vessels entering a human heart and from a right atrium of the heart are also included within the scope of the invention.
During open heart surgery and in other applications where it is desired to assist the circulatory system, a cardiopulmonary bypass machine is generally used to temporarily assume the functions of a heart and lungs. To accomplish this, tubes, known as catheters, are generally inserted into the major blood vessels entering and exiting the heart. These catheters, in turn, are connected to the cardiopulmonary bypass machine. Blood entering the heart is picked up by a catheter and directed to the cardiopulmonary bypass machine. The machine oxygenates the blood and pumps it back, through another catheter, into the major blood vessels exiting the heart. In this manner, the heart and lungs are bypassed, and the blood is still oxygenated and pumped through a patient.
The blood being bypassed is generally referred to as systemic blood. It is the blood that normally circulates from a side of the heart, through the patient generally, and returns to a right side of the heart through a superior and an inferior vena cava. Systemic blood is to be distinguished from coronary blood which circulates from the left side of the heart, through the coronary arteries and the coronary veins of the heart muscle itself, and returns to the right side of the heart through a coronary sinus. The coronary sinus is located within the right atrium of the heart.
Coronary blood, as opposed to systemic blood, is generally interrupted rather than bypassed. This interruption of blood flow can cause extensive damage to the myocardium. Several methods of providing protection for the myocardium have been developed. A common method is cold cardioplegic arrest of the heart.
The use of cold cardioplegic solutions containing high levels of potassium is a routine part of many cardiac operations. Its primary purpose is to protect the myocardium from ischemic damage during periods of coronary artery interruption. The cardioplegic solution is infused into the root of the aorta or directly into the coronary arteries from which it is then distributed throughout the myocardial muscle by the coronary arterial network. Ultimately, the cardioplegic solution drains into the right atrium of the heart through the coronary sinus.
The used cardioplegic solution entering the right atrium can generally be dealt with in either of two ways. It can be allowed to mix with the systemic blood and directed to the cardiopulmonary bypass machine, or it can be separately removed from the patient. An example of allowing mixing is disclosed in U.S. Pat. No. 4,129,129. A catheter having a small diameter inlet opening, extending beyond a main catheter entrance area, assists in the maintenance of adequate venous drainage by collecting venous blood directly from the inferior vena cava. The main catheter entrance collects the flow from the superior vena cava and the coronary sinus.
Mixing the cardioplegic solution with the blood can have disadvantages. Depending upon the cardioplegic solution used, hemodilution and hyperkalemia are two known side effects. Excessive hemodilution decreases the oxygen carrying capacity of the blood by lowering the hemoglobin levels. It also contributes to bleeding complications by decreasing the concentrations of clotting factors in the blood. Hyperkalemia has been associated with difficulties in restoring the electromechanical activity of the heart after open heart surgery.
Removing the used cardioplegic solution from the patient minimizes these side effects. One such method is described in "Method of Discarding Cardioplegic Solution via the Right Atrium," by John H. Rousou, M.D., and Richard M. Engelman, M.D., Journal of Thorasic Cardiovascular Surgery, 82:938-942, 1981. As shown in FIG. 1, the authors drain the vena cavae through two separate catheters inserted through the right atrium. An additional suture opening is made in the right atrium to provide an entry site for a third catheter. The third catheter is used to suction the cardioplegic solution draining into the right atrium through the coronary sinus. While this approach restricts mixing of the cardioplegic solution with the systemic blood, it prolongs and complicates the surgery by requiring the insertion of the third catheter through a third wound in the heart. The catheters and methods of the present invention overcome these disadvantages to achieve separate venous and coronary sinus drainage without the complication or trauma associated with the third catheter and the third wound in the heart.